Dilated blood vessels in the lung may explain low oxygen levels in
severe cases of COVID-19

Date:
August 20, 2020
Source:
The Mount Sinai Hospital / Mount Sinai School of Medicine
Summary:
A new pilot study suggests that COVID-19 is causing significant
dilation of the blood vessels of the lung, specifically the
capillaries.



FULL STORY ==========================================================================
A new pilot study from the Icahn School of Medicine at Mount Sinai
suggests that COVID-19 is causing significant dilation of the blood
vessels of the lung, specifically the capillaries. This vasodilation is contributing to the very low oxygen levels seen in COVID-19 respiratory
failure and also helps explain why the disease behaves differently
than classic acute respiratory distress syndrome (ARDS). The study
was published in the American Journal of Respiratory and Critical Care Medicine.


==========================================================================
In classical ARDS, pulmonary inflammation leads to leaky pulmonary blood vessels that flood the lungs with fluid, making the lungs stiff and
impairing oxygenation. Many patients with COVID-19 pneumonia demonstrate
severe hypoxemia that is markedly out of proportion to the degree of
lung stiffness. This disconnect between gas exchange and lung mechanics
in COVID-19 pneumonia has raised the question of whether the mechanisms
of hypoxemia in COVID-19 differ from those in classical ARDS.

The discovery was serendipitous. Researchers were initially assessing
cerebral blood flow in mechanically ventilated COVID-19 patients with
altered mental status to look for, among other things, abnormalities
consistent with stroke.

They used a robotic transcranial Doppler (TCD), the Lucid Robotic System
by NovaSignal, to perform a "bubble study," which is a non-invasive and painless ultrasound technique.

"It is remarkable that a diagnostic machine used to study the brain could
give us insight into the pathophysiology of a pulmonary disease. The
benefit of using this particular system was that automated monitoring
allowed providers to assess cerebral blood flow while minimizing
the potential for exposure to COVID-19," said Alexandra Reynolds, MD,
Assistant Professor of Neurosurgery, and Neurology, at the Icahn School
of Medicine at Mount Sinai and Director of TeleNeurocritical Care for
the Mount Sinai Health System.

During this study, agitated saline -- saline with tiny microbubbles --
is injected into the patient's vein and TCD is used to determine if
those microbubbles appear in the blood vessels of the brain. Under normal circumstances, these microbubbles would travel to the right side of the
heart, enter the blood vessels of the lungs, and ultimately get filtered
by the pulmonary capillaries, because the diameter of the microbubbles is bigger than the diameter of the pulmonary capillaries. If the microbubbles
are detected in the blood vessels of the brain, it implies that either
there is a hole in the heart, so that blood can travel from the right to
the left side of the heart without going through the lungs, or that the capillaries in the lungs are abnormally dilated, allowing the microbubbles
to pass through.

In the pilot study, 18 mechanically ventilated patients with severe
COVID-19 pneumonia underwent TCD with bubble study. Fifteen out of the
18 (83 percent) patients had detectable microbubbles, indicating the
presence of abnormally dilated pulmonary blood vessels. The number
of microbubbles detected by the TCD correlated with the severity of
hypoxemia, indicating that the pulmonary vasodilations may explain
the disproportionate hypoxemia seen in many patients with COVID-19
pneumonia. Previous studies have demonstrated that only 26 percent of
patients with classical ARDS have microbubbles during a bubble study; furthermore, the number of these microbubbles does not correlate with
the severity of hypoxemia, implying that pulmonary vascular dilations
are not a major mechanism of hypoxemia in classical ARDS.

"It is becoming more evident that the virus wreaks havoc on the pulmonary vasculature in a variety of ways. This study helps explain the strange phenomenon seen in some COVID-19 patients known as 'happy hypoxia,'
where oxygen levels are very low, but the patients do not appear to
be in respiratory distress. If these findings are confirmed in larger
studies, pulmonary microbubble transit may potentially serve as a marker
of disease severity or even a surrogate endpoint in therapeutic trials for COVID-19 pneumonia. Future studies that investigate the use of pulmonary vascular constrictors in this patient population may be warranted,"
says senior author Hooman Poor, MD, Assistant Professor of Medicine
(Pulmonary, Critical Care and Sleep Medicine) at the Icahn School of
Medicine at Mount Sinai and Director of Pulmonary Vascular Disease at
the Mount Sinai -- National Jewish Health Respiratory Institute.

The pilot study has since expanded to collect data from approximately
80 patients, including those with less severe disease, and will evaluate
the severity of microbubble transit and how it varies during the course
of the disease.


========================================================================== Story Source: Materials provided by The_Mount_Sinai_Hospital_/_Mount_Sinai_School_of Medicine. Note: Content
may be edited for style and length.


========================================================================== Journal Reference:
1. Alexandra S. Reynolds, Alison G Lee, Joshua Renz, Katherine
DeSantis,
John Liang, Charles A Powell, Corey E Ventetuolo, Hooman D. Poor.

Pulmonary Vascular Dilatation Detected by Automated Transcranial
Doppler in COVID-19 Pneumonia. American Journal of Respiratory
and Critical Care Medicine, 2020; DOI: 10.1164/rccm.202006-2219LE ==========================================================================

Link to news story: https://www.sciencedaily.com/releases/2020/08/200820143856.htm

--- up 5 weeks, 1 day, 1 hour, 55 minutes
* Origin: -=> Castle Rock BBS <=- Now Husky HPT Powered! (1337:3/111)